clojure.core/ex-cause

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Type: function Added: Clojure 1.10 Examples: 2 Runnable: 0

([ex])

Returns the cause of ex if ex is a Throwable. Otherwise returns nil.

Examples

by loeschzwerg on 2021-11-12 . May have evaluation errors. ▶

;; (ex-cause e) gives you the next linked exception in an Exception-chain ;; Use (def a 1) ;;=> #'user/a (def b 0) ;;=> #'user/b (def chain (try (/ a b) (catch ArithmeticException ae (ex-info ;; contextualize ae with ExceptionInfo "Send help, please" {:divisor a :divident b} ae)))) ;;=> #'user/chain chain ;;=> ;#error{:cause "Divide by zero", ; :via [{:type clojure.lang.ExceptionInfo, ; :message "Send help, please", ; :data {:divisor 1, :divident 0}, ; :at [...]} ; {:type java.lang.ArithmeticException, ; :message "Divide by zero", ; :at [clojure.lang.Numbers divide "Numbers.java" 188]}], ; :trace [[clojure.lang.Numbers divide "Numbers.java" 188] ; [...] ; [java.lang.Thread run "Thread.java" 829]]} (ex-cause chain) ;;=> ;#error{:cause "Divide by zero", ; :via [{:type java.lang.ArithmeticException, ;; <-- ae is first. ; :message "Divide by zero", ; :at [clojure.lang.Numbers divide "Numbers.java" 188]}], ; :trace [[clojure.lang.Numbers divide "Numbers.java" 188] ; [...]

by loeschzwerg on 2021-11-15 . May have evaluation errors. ▶

;; You can use ex-cause to extract the messages of a chain: (defn ex-msg-chain [ex delimiter] (->> ex (iterate ex-cause) (take-while some?) (mapv ex-message) (interpose delimiter) (apply str)) ;;=> #'user/ex-msg-chain ;; Let's try this on a simple chained Exception (def chained-ex (ex-info "top-level" {:level 1} (ex-info "sec-level" {:level 2} (ex-info "low-level" {:level 3})))) ;;=> #'user/chained-ex (ex-msg-chain chained-ex " -> ") ;;=> "top-level -> sec-level -> low-level"

See also

• clojure.core/ex-info (0)
• clojure.core/ex-data (1)
• clojure.core/ex-message

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